Currently, Long Term Evolution (LTE) communication networks are deployed to operate in licensed carriers. With the development of LTE, some companies have proposed research topics on deployment of LTE in unlicensed carriers. For example, some companies believe that, with the rapid growth of data traffic, in near future the licensed carriers would not be sufficient to carry the huge amount of data brought by such rapid growth of traffic. It has been proposed to deploy LTE in unlicensed carriers, such that some of the data traffic in the licensed carriers can be offloaded to the unlicensed carriers, thereby mitigating the data traffic load due to the traffic growth. Meanwhile, the unlicensed carriers have the following characteristics. In one hand, the unlicensed carriers do not need to be purchased or the carrier resources have zero cost, so the unlicensed carriers free or inexpensive. On the other hand, the unlicensed carriers can be deployed by both individuals and companies and vendor devices can be used, so they have low admission requirements. Furthermore, the unlicensed carriers can be shared. When several different systems or several different operators of one single system operate in the unlicensed carriers, carrier efficiency can be improved by means of resource sharing.
While it is obviously advantageous to deploy LTE in the unlicensed carriers, there are problems in such deployment. For example, there are many radio access technologies, leading to problems such as difficulties in coordination across different communication standards and diversities in network topologies. Further, there are many radio access stations, leading to problems such as a large number of users, a difficult coordination and a high overhead in centralized management. As there are many radio access technologies, there will be various radio systems in the unlicensed carriers, which are difficult to coordinate and will cause severe interference. Hence, when the LTE is deployed in the unlicensed carriers, there will still be mutual interference between neighboring stations that are contending for the unlicensed carriers.
In order to solve these problems, when the LTE is deployed in the unlicensed carriers, it is required to support control of the unlicensed carriers. It is required by most countries to support a Listen Before Talk (LBT) mechanism when the system is deployed in the unlicensed carriers. With the LBT mechanism, it is possible to avoid mutual interference between neighboring systems that are using the unlicensed carriers simultaneously. Meanwhile, a contention back-off mechanism can be introduced optionally. That is, with the contention back-off mechanism, for neighboring system stations (typically neighboring transmitting nodes within one single system), it is possible to avoid the interference caused by neighboring transmitting nodes of the same system that are using the unlicensed carriers simultaneously.
At present, the LTE is working on researches on deployment of the LTE in a Licensed-Assisted Access (LAA) system. Most companies believe that a contention-based back-off mechanism will be adopted in a downlink in the LAA system for contending for access to an unlicensed carrier. For example, FIG. 1 is a flowchart illustrating an LBT mechanism in a cat4-based process (referring to specifications regarding cat4 in 3GPP TR 36.899). For an LBT mechanism in a cat2-based process (referring to specifications regarding cat2 in 3GPP TR 36.899), one single Clear Channel Assessment (CCA) having a fixed time length can be used. When a clear channel is detected, access to the unlicensed carrier is obtained. Alternatively, a number of successive CCAs each having a predefined time length can be performed. When the first CCA fails, the subsequent CCAs can be performed. The access to the unlicensed carrier can be obtained when any one of the CCAs is successful.
Further, it has been found in the researches that, while neighboring stations in one system can contend for the same unlicensed carriers, due to lack of a coordination mechanism, the neighboring stations contend for the unlicensed carriers independently from each other and thus there may be mutual interference between neighboring unlicensed carriers occupied by the neighboring stations due to adjacent frequency leakage.
There are currently no effective solutions to the problem in the related art associated with interference due to unlicensed carrier contention by neighboring stations.